PART 1 Special risks groups - Pregnancy Flashcards
During pregnancy, most drugs can ____ and _____.
Cross the placenta and expose the baby to their effects.
Factors affecting placental drug transfer and drug effects on the fetus
- Drug physiochemical properties.
- Duration of drug exposure.
- Distribution in different fetal tissues.
- Stage of placental and fetal development.
- Effects of drugs used in combination.
- Rate at which drug crosses placenta and amount reaching fetus.
Pharmacokinetic changes in GASTROINTESTINAL ABSORPTION
- Decreased GI motility and reduction in gastric acid secretion.
- Increase in gastric pH, therefore negatively affects drugs that require acidic pH for absorption.
- Nausea and vomiting
Pharmacokinetic changes in LUNG ABSORPTION
- Cardiac and tidal volumes increase by approx. 50% in pregnancy.
- Hyperventilation and increased pulmonary blood flow.
Pharmacokinetic changes in TRANSDERMAL ABSORPTION
- Vasodilatation leads to increased tissue perfusion.
- Absorption on IM administration is highly effective.
Factors affecting DRUG ABSORPTION in Pregnancy.
Hint - LMP
- Lipid solubility
- Molecular size
- pH
Lipid solubility factor
- Lipid soluble drugs (e.g. Thiopental) easily diffuse across the placenta.
- Impermeability of the placenta to polar compounds is relative rather than absolute (whole thing).
- That’s if high enough maternal-fetal concentration gradients are achieved, polar compounds cross the placenta in measurable amounts (e.g. Salicylate).
Molecular size factor
- Influences the rate of transfer and amount of transfer.
- Drugs having molecular weight:
A. 250-500 cross easily.
B. 500-1000 cross with more difficulty.
C. >1000 cross very poorly.
Factors affecting DRUG DISTRIBUTION in pregnancy.
- Protein binding
- Body fat
- Total body water
Total body water factor
Total body water increases due to hemodilution, so large volume of distribution for water soluble drugs.
Total body water factor
Total body water increases due to hemodilution, so large volume of distribution for water soluble drugs.
Body fat factor
- Body fat is increased and acts as a reservoir for lipid soluble drugs.
- These lipid soluble drugs can increase and accumulate in body fat, causing toxicity.
Factors affecting DRUG METABOLISM in pregnancy
- Blood flow (cardiac output)
- Hepatic clearance
Blood flow factor
Hepatic metabolism is increased through blood flow to liver.
Hepatic clearance factor
- Hepatic clearance = ability of the liver to extract and metabolize a drug as it passes through the liver.
- Drugs metabolized by the liver have increased clearance.
